fix: DDL type fallback in insert_rows when DESCRIBE TABLE returns empty

If _get_column_info fails silently (returns {}), convert_value had no type
info and passed string values through unconverted — causing 22018 on every
row for any numeric column.

- Add ddl_types param to insert_rows: {COL_UPPER: DDL_TYPE} from LegitData schema
- convert_value uses ddl_types as fallback when column not in column_info
- Log warning when column_info is empty so future failures are visible
- Pass ddl_types from generate() at the call site

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

legitdata_bridge.py

@@ -172,20 +172,26 @@ class KeyPairSnowflakeWriter:
             self.connection = None
             print("Disconnected from Snowflake")
     
-    def insert_rows(self, table_name: str, columns: list, rows: list, batch_size: int = 1000) -> int:
-        """Insert rows into a Snowflake table."""
+    def insert_rows(self, table_name: str, columns: list, rows: list, batch_size: int = 1000, ddl_types: dict = None) -> int:
+        """Insert rows into a Snowflake table.
+
+        ddl_types: optional dict of {COLUMN_NAME_UPPER: DDL_DATA_TYPE} from the LegitData schema,
+        used as fallback when DESCRIBE TABLE (column_info) doesn't have a column.
+        """
         from decimal import Decimal
         from datetime import datetime, date
-        
+
         if not rows:
             return 0
-        
+
         if not self.cursor:
             raise RuntimeError("Not connected to database")
         
         # Get column metadata for this table to know constraints
         column_info = self._get_column_info(table_name)
-        
+        if not column_info:
+            print(f"WARNING: column_info empty for {table_name} — DESCRIBE TABLE failed, falling back to DDL types")
+
         # Filter out identity columns (let Snowflake auto-generate)
         filtered_columns = []
         filtered_indices = []
@@ -232,6 +238,10 @@ class KeyPairSnowflakeWriter:
             if col_upper in column_info:
                 info = column_info[col_upper]
                 data_type = info.get('type', '')
+            elif ddl_types and col_upper in ddl_types:
+                # Fallback: use DDL-declared type when DESCRIBE TABLE didn't return this column
+                info = {}
+                data_type = ddl_types[col_upper].upper()
                 
                 # Truncate strings to fit VARCHAR length
                 if 'VARCHAR' in data_type or 'TEXT' in data_type:
@@ -476,8 +486,11 @@ class DemoLegitGenerator:
                 
                 if truncate_first:
                     writer.truncate_table(table.name)
-                
-                count = writer.insert_rows(table.name, columns, list_rows)
+
+                # Build DDL type map as fallback for convert_value when DESCRIBE TABLE fails
+                ddl_types = {col.name.upper(): (col.data_type or '').upper()
+                             for col in table.columns}
+                count = writer.insert_rows(table.name, columns, list_rows, ddl_types=ddl_types)
                 results[table.name] = count
         
         return results